A method for characterizing the microstructure and magnetic properties of a permanent magnet material

Abstract

The present invention discloses a method for characterizing the microstructure and magnetic properties of a permanent magnet material, belonging to the technical field of permanent magnet materials, and solving the problem that the detection of the microstructure and magnetic properties of existing permanent magnet materials requires specific instruments for detection respectively, and the detection time is relatively long. The characterization method includes: collecting microscopic morphology photos of different positions of the permanent magnet material; calculating the fractal dimension of the microscopic morphology photos by using the fractal dimension calculation method; judging the uniformity, isotropy or anisotropy, and magnetic properties of the permanent magnet material according to the fractal dimensions of the microscopic morphology photos at different positions; wherein, the uniformity of the permanent magnet material is judged according to the absolute value of the difference between the fractal dimensions of the microscopic morphology photos at different positions on the same plane; the isotropy or anisotropy and magnetic properties of the permanent magnet material are judged according to the absolute value of the difference between the fractal dimensions in the vertical orientation direction and the parallel orientation direction of the material. The method of the present invention requires less equipment, is simple, fast, and the result is accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of permanent magnet materials, and particularly relates to a method for characterizing the microstructure and magnetic properties of permanent magnet materials. Background Art

[0002] Permanent magnet materials are of great significance as a magnetic energy storage material. After being magnetized once, it can continuously provide an external magnetic field without the need for external energy to maintain.

[0003] The magnetic properties of permanent magnet materials have an important impact on their performance in various applications. For example, in wind power generation, the magnetic properties of permanent magnets directly affect the efficiency and stability of the motor; in electric vehicles, the magnetic properties of permanent magnets are related to the output torque and driving range of the motor; in nuclear magnetic resonance imaging, the magnetic properties of permanent magnets determine the clarity and accuracy of imaging. During the preparation process of permanent magnet materials, by optimizing manufacturing process parameters such as melting, powder making, forming, and sintering, the influence of composition, grain size, and surface defects on magnetic properties can be reduced. The detection of the microstructure and magnetic properties of permanent magnet materials requires specific instruments for detection respectively, and the detection time is relatively long. Therefore, how to provide a method for quickly characterizing the microstructure and magnetic properties of permanent magnet materials has important application value for the research and production of permanent magnet materials. Summary of the Invention

[0004] In view of the above situation, the present invention aims to provide a method for characterizing the microstructure and magnetic properties of permanent magnet materials, which is used to solve at least one of the following technical problems: the existing detection of the microstructure and magnetic properties of permanent magnet materials requires specific instruments for detection respectively, and the detection time is relatively long.

[0005] The object of the present invention is mainly achieved through the following technical solutions:

[0006] On the one hand, the present invention provides a method for characterizing the microstructure and magnetic properties of permanent magnet materials, and the characterization method includes:

[0007] Collecting microtopography photos of different positions of the permanent magnet material;

[0008] Calculating the fractal dimension of the microtopography photos by using the fractal dimension calculation method;

[0009] Judging the uniformity, isotropy or anisotropy, and magnetic properties of the permanent magnet material according to the fractal dimensions of the microtopography photos at different positions;

[0010] Among them, the uniformity of the permanent magnet material is judged according to the absolute value of the difference between the fractal dimensions of the microtopography photos at different positions on the same plane; the isotropy or anisotropy and magnetic properties of the permanent magnet material are judged according to the absolute value of the difference between the fractal dimensions in the vertical orientation direction and the parallel orientation direction of the material.

[0011] Furthermore, the magnetic properties mainly include remanence and coercivity.

[0012] Furthermore, the method for judging the uniformity by the absolute value δ of the difference in the fractal dimension of the microscopic morphology photos at different positions on the same plane includes:

[0013] 0 ≤ δ ≤ 0.02, the permanent magnet material is uniform;

[0014] δ > 0.02, the permanent magnet material is non-uniform.

[0015] Furthermore, the method for judging the isotropy or anisotropy of the permanent magnet material according to the absolute value Δ of the difference in the fractal dimension between the vertical orientation direction and the parallel orientation direction of the material includes:

[0016] Δ ≥ 0.03, the permanent magnet material is anisotropic;

[0017] 0 ≤ Δ ≤ 0.03, the permanent magnet material is isotropic.

[0018] Furthermore, the method for judging the magnetic properties of the permanent magnet material according to the absolute value Δ of the difference in the fractal dimension between the vertical orientation direction and the parallel orientation direction of the material includes:

[0019] Δ ≥ 0.05, the permanent magnet material has high remanence and low coercivity;

[0020] 0.03 ≤ Δ < 0.05, the permanent magnet material has high coercivity and low remanence.

[0021] Furthermore, the permanent magnet material includes rare earth permanent magnet materials, ferrite permanent magnet materials or alnico permanent magnet materials.

[0022] Furthermore, the microscopic morphology is the microscopic morphology of a fracture specimen, a crack and / or a planar metallographic specimen.

[0023] Furthermore, the microscopic morphology is observed using one or more of an optical microscope, a scanning electron microscope, a magnetic force microscope, and a transmission electron microscope.

[0024] Furthermore, the calculation of the fractal dimension for the microscopic morphology photos includes: first, the obtained microscopic morphology photos are binarized through a computer-aided program, and the information of the picture is converted into a matrix containing only 0 and 1; then, image processing technology is used to process and analyze the image, thereby obtaining the fractal dimension.

[0025] Furthermore, the image processing technology includes the direct counting method, the box counting method, the differential box method, and the small vein method.

[0026] Compared with the prior art, the present invention can at least achieve one of the following beneficial effects:

[0027] The method for characterizing the microstructure and magnetic properties of the permanent magnet material of the present invention can obtain the characterization of the uniformity, isotropy or anisotropy, and magnetic properties of the permanent magnet material through the analysis of the microtopography photos at different positions of the permanent magnet material. The required equipment is less, the method is simple and fast, and it can quickly provide a comprehensive characterization of the permanent magnet material.

[0028] The method for characterizing the microstructure and magnetic properties of the permanent magnet material of the present invention has accurate characterization results and strong repeatability through the selection of microtopography photos and the choice of observation equipment, and can conveniently and quickly provide a comprehensive characterization of the permanent magnet material.

[0029] Other features and advantages of the present invention will be described in the subsequent specification, and some of them will be obvious from the specification or understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the content specifically pointed out in the written specification and the drawings. Brief Description of the Drawings

[0030] The drawings are only for the purpose of showing specific embodiments and are not considered to be a limitation of the present invention. Throughout the drawings, the same reference signs denote the same components;

[0031] Figure 1 Scanning electron microscope photos, processed binary images, data fitting of different box side lengths, and fractal dimensions of different box side lengths at a position parallel to the orientation direction on the fracture surface of Example 1;

[0032] Figure 2 Scanning electron microscope photos, processed binary images, data fitting of different box side lengths, and fractal dimensions of different box side lengths at a second position parallel to the orientation direction on the fracture surface of Example 1;

[0033] Figure 3 Scanning electron microscope photos, processed binary images, data fitting of different box side lengths, and fractal dimensions of different box side lengths at a position perpendicular to the orientation direction on the fracture surface of Example 1;

[0034] Figure 4 Scanning electron microscope photos, processed binary images, data fitting of different box side lengths, and fractal dimensions of different box side lengths at a second position perpendicular to the orientation direction on the fracture surface of Example 1;

[0035] Figure 5 Scanning electron microscope photos, processed binary images, data fitting of different box side lengths, and fractal dimensions of different box side lengths at a position parallel to the orientation direction on the fracture surface of Example 2;

[0036] Figure 6SEM photos at two positions parallel to the orientation direction on the fracture surface of Example 2, the processed binary images, data fitting for different box side lengths, and fractal dimensions for different box side lengths;

[0037] Figure 7 SEM photos at one position perpendicular to the orientation direction on the fracture surface of Example 2, the processed binary images, data fitting for different box side lengths, and fractal dimensions for different box side lengths;

[0038] Figure 8 SEM photos at two positions perpendicular to the orientation direction on the fracture surface of Example 2, the processed binary images, data fitting for different box side lengths, and fractal dimensions for different box side lengths;

[0039] Figure 9 SEM photos at one position parallel to the orientation direction on the fracture surface of Example 3, the processed binary images, data fitting for different box side lengths, and fractal dimensions for different box side lengths;

[0040] Figure 10 SEM photos at two positions parallel to the orientation direction on the fracture surface of Example 3, the processed binary images, data fitting for different box side lengths, and fractal dimensions for different box side lengths;

[0041] Figure 11 SEM photos at one position perpendicular to the orientation direction on the fracture surface of Example 3, the processed binary images, data fitting for different box side lengths, and fractal dimensions for different box side lengths;

[0042] Figure 12 SEM photos at two positions perpendicular to the orientation direction on the fracture surface of Example 3, the processed binary images, data fitting for different box side lengths, and fractal dimensions for different box side lengths;

[0043] Figure 13 EBSD photos at position one perpendicular to the orientation direction of Example 4, the processed binary images, data fitting for different box side lengths, and fractal dimensions for different box side lengths;

[0044] Figure 14 EBSD photos at position two perpendicular to the orientation direction of Example 4, the processed binary images, data fitting for different box side lengths, and fractal dimensions for different box side lengths;

[0045] Figure 15 EBSD photos at position one parallel to the orientation direction of Example 4, the processed binary images, data fitting for different box side lengths, and fractal dimensions for different box side lengths;

[0046] Figure 16EBSD photographs, processed binary images, data fitting with different box side lengths, and fractal dimensions with different box side lengths at position two parallel to the orientation direction in Example 4. Detailed implementation mode

[0047] The preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings, in which the accompanying drawings form a part of the present invention and are used together with the embodiments of the present invention to explain the principles of the present invention.

[0048] The present invention provides a method for characterizing the microstructure and magnetic properties of a permanent magnet material. The above characterization method includes the following steps:

[0049] Collect microtopography photographs of different positions of the permanent magnet material;

[0050] Use the fractal dimension calculation method to calculate the fractal dimension of the microtopography photographs;

[0051] Judge the uniformity, isotropy or anisotropy, and magnetic properties of the permanent magnet material according to the fractal dimensions of the microtopography photographs at different positions;

[0052] Judge the uniformity of the permanent magnet material according to the absolute value of the difference in fractal dimensions of the microtopography photographs at different positions on the same plane;

[0053] Judge the isotropy or anisotropy and magnetic properties of the permanent magnet material according to the absolute value of the difference in fractal dimensions between the perpendicular orientation direction and the parallel orientation direction of the material.

[0054] Specifically, the above permanent magnet material includes rare earth permanent magnet materials, ferrite permanent magnet materials, or alnico permanent magnet materials.

[0055] Specifically, the above rare earth permanent magnet materials include samarium cobalt magnets, neodymium iron boron magnets, or cerium magnets.

[0056] Specifically, the above microtopography may be the microtopography of a fracture specimen, crack, and / or planar metallographic specimen.

[0057] Specifically, the above microtopography photographs can be obtained by microscopically observing a fracture specimen or a planar metallographic specimen using observation devices such as an optical microscope, a scanning electron microscope, a magnetic force microscope, or a transmission electron microscope. Clear grains, grain boundaries, cellular phases, cell walls, etc. of the permanent magnet material can be observed using an optical microscope. The magnification of a scanning electron microscope is much higher than that of an optical microscope, so it can form a higher resolution and a larger magnification. The magnification of an electron microscope can reach hundreds of thousands of times or even higher.

[0058] Specifically, the above microtopography may include one or more of a scanning electron microscope microstructure topography, a magnetic force microscope magnetic domain topography, an electron backscatter diffraction microtopography, and a transmission electron microscope topography.

[0059] Preferably, in combination with the morphological characteristics of the detection equipment and different specimens, the above-mentioned microscopic morphology may be the scanning electron microscope microstructure morphology of the fracture specimen and / or the electron backscatter diffraction microscopic morphology of the plane metallographic specimen.

[0060] Specifically, the above-mentioned fracture specimen is obtained by using a universal testing machine through tension, compression, bending, shearing, torsion or impact.

[0061] Preferably, the above-mentioned fracture specimen is obtained by compression using a universal testing machine.

[0062] Preferably, during the process of preparing the above-mentioned fracture specimen using a universal testing machine, the sample needs to be correctly installed in the fixture of the testing machine to ensure that the sample can be evenly stressed during the test, and the tightening degree of the fixture is adjusted to avoid damage to the sample due to the fixture being too tight or too loose before the test.

[0063] Specifically, after cleaning the fracture of the above-mentioned fracture specimen with a cleaning agent (such as acetone, alcohol, etc.), it is observed with a scanning electron microscope to obtain the scanning electron microscope microstructure morphology of the fracture specimen.

[0064] Specifically, during the cleaning process of the above-mentioned fracture specimen, it is necessary to ensure that the microscopic structure of the fracture is not damaged for subsequent observation and analysis.

[0065] Specifically, the above-mentioned plane metallographic specimen can be prepared by steps such as grinding, polishing, and metallographic corrosion.

[0066] Specifically, the above-mentioned plane metallographic specimen needs to ensure a smooth surface for subsequent observation and analysis.

[0067] Specifically, the calculation of the fractal dimension for the microscopic morphology photos includes: first, the obtained microscopic morphology photos are binarized through a computer-aided program, and the information of the picture is converted into a matrix containing only 0 and 1; then, image processing technology is used to process and analyze the image to obtain the fractal dimension.

[0068] Specifically, the above-mentioned computer-aided program includes but is not limited to MATLAB, and also includes, for example, high-level technical computing languages and interactive environments for algorithm development, data visualization, data analysis, and numerical calculations.

[0069] Specifically, the above-mentioned image processing technology includes but is not limited to the direct counting method, box counting method, differential box method, and small vein method.

[0070] Specifically, the above image processing technology uses the box-counting method, which includes: dividing the image into boxes with side length δk, where k = 1, 2, 4, ..., that is, the side lengths of the boxes are 1, 2, 4, ... in sequence. Calculate the number of image information (0 or 1) contained in each box. If a box contains at least one 1, it is considered that the box contains image information. Record the number Nk of boxes containing image information. In the double logarithmic coordinate plane, use the least squares method to fit the data points (logδk, logNk) with a straight line. The negative value D of the slope of the obtained straight line is the fractal dimension of the image.

[0071] Specifically, the above magnetic properties mainly include remanence and coercivity.

[0072] Specifically, based on the fact that the surface topography of the permanent magnet material has a self-similar fractal structure, when collecting microscopic topography photos at different positions of the permanent magnet material, the magnification can be different.

[0073] Specifically, the calculation of the fractal dimension is obtained according to the self-similarity of the microscopic topography. The corresponding fractal dimensions are calculated from the photos of the microscopic topography at different positions. The consistency of the fractal dimensions at different positions on the same plane can be used as a condition for judging uniformity. The absolute value δ of the difference between the fractal dimensions of the microscopic topography photos at two different positions and the method for judging uniformity are as follows:

[0074] 0 ≤ δ ≤ 0.02 indicates that the permanent magnet material is uniform;

[0075] δ > 0.02 indicates that the permanent magnet material is non-uniform.

[0076] Specifically, if the permanent magnet material is anisotropic, the microscopic topographies in the parallel orientation direction and the perpendicular orientation direction are different. The isotropy or anisotropy of the permanent magnet material is judged according to the absolute value Δ of the difference between the fractal dimensions in the perpendicular orientation direction and the parallel orientation direction of the material. On the basis that the permanent magnet material is anisotropic, by taking the fractal dimensions in the two directions as the structure factors for describing the microscopic topography of the permanent magnet material and combining the empirical formulas of coercivity and remanence, the magnetic properties of the permanent magnet material can be judged. The specific judgment method is as follows:

[0077] Δ ≥ 0.03 indicates that the permanent magnet material is anisotropic; and then judge the high or low coercivity and remanence of the permanent magnet material;

[0078] 0 ≤ Δ ≤ 0.03 indicates that the permanent magnet material is isotropic;

[0079] Δ ≥ 0.05 indicates that the permanent magnet material has high remanence and low coercivity;

[0080] 0.03 ≤ Δ < 0.05 indicates that the permanent magnet material has high coercivity and low remanence.

[0081] Specifically, the above-mentioned high remanence refers to the remanence in the range of 14.0 kGs to 15.5 kGs, and the low coercivity refers to the coercivity in the range of 8.0 kOe to 14.0 kOe; the low remanence refers to the remanence in the range of 10.0 kGs to 14.0 kGs (excluding 14.0 kGs); the high coercivity refers to the coercivity in the range of 14.0 kOe to 45.0 kOe (excluding 14.0 kOe).

[0082] The present invention also provides a device for characterizing the microstructure and magnetic properties of a permanent magnet material, including an automatic feeding device for the permanent magnet material, a sample preparation grinding and polishing component for the permanent magnet material, a device for observing the surface topography of the permanent magnet material sample, a data acquisition device, and a fractal dimension calculation system. This device integrates the sample preparation, topography observation, data acquisition, and calculation of the fractal dimension of the permanent magnet material, and can conveniently and quickly obtain the microtopography and magnetic properties.

[0083] The method for characterizing the microstructure and magnetic properties of the permanent magnet material of the present invention can obtain the characterization of the uniformity, isotropy or anisotropy, and magnetic properties of the permanent magnet material through the analysis of the microtopography photos at different positions of the permanent magnet material. The required equipment is less, the method is simple and fast, and it can quickly provide a comprehensive characterization of the permanent magnet material.

[0084] The method for characterizing the microstructure and magnetic properties of the permanent magnet material of the present invention has accurate characterization results and strong repeatability through the selection of microtopography photos and the choice of observation equipment, and can conveniently and quickly provide a comprehensive characterization of the permanent magnet material.

[0085] The following takes specific embodiments to demonstrate the advantages of the method of the present invention.

[0086] Example 1

[0087] This embodiment provides a method for characterizing the microstructure and magnetic properties of a permanent magnet material. The permanent magnet material in this embodiment is a NdFeB permanent magnet of N50 grade. The method in this embodiment includes the following steps:

[0088] Step 1: Compress the specimen with a universal mechanical testing machine to obtain a fractured specimen;

[0089] Step 2: Clean the fracture with acetone;

[0090] Step 3: Observe the fracture with a scanning electron microscope, and collect microtopography photos at different positions parallel to the orientation direction and microtopography photos at different positions perpendicular to the orientation direction;

[0091] Step 4: Calculate the fractal dimension of the microtopography photos by using the fractal dimension calculation method;

[0092] Step 5: Evaluate the uniformity, isotropy or anisotropy, and magnetic properties of the permanent magnet material based on the fractal dimensions of the microscopic morphology photos at different positions. The fractal dimensions at different positions in two directions are used to judge the uniformity, and the average of the fractal dimensions at different positions in two directions is used to judge the isotropy or anisotropy and evaluate the magnetic properties;

[0093] Figure 1 and Figure 2 are the results of position one and position two randomly selected on the fracture surface of Example 1 parallel to the orientation direction, respectively. Among them, (a) is the scanning electron microscope photo, (b) is the binary image after image processing using the box-counting method, (c) is the data fitting of different box side lengths after image processing using the box-counting method, and (d) is the fractal dimension of different box side lengths after image processing using the box-counting method; among them, the scanning electron microscope photo includes a gray main phase and a bright white rare-earth-rich grain boundary phase.

[0094] Figure 3 and Figure 4 are the results of position one and position two randomly selected on the fracture surface of Example 1 perpendicular to the orientation direction, respectively. Among them, (a) is the scanning electron microscope photo, (b) is the binary image after image processing using the box-counting method, (c) is the data fitting of different box side lengths after image processing using the box-counting method, and (d) is the fractal dimension of different box side lengths after image processing using the box-counting method; among them, the scanning electron microscope photo includes a gray main phase and a bright white rare-earth-rich grain boundary phase.

[0095] From Figure 1 and Figure 2 , it can be seen that the fractal dimensions at different positions parallel to the orientation direction are 1.7360 and 1.7476 respectively, and the difference in fractal dimensions is within the range of 0 < δ ≤ 0.02, indicating that the magnet of Example 1 is uniform in the direction parallel to the orientation.

[0096] From Figure 3 and Figure 4 , it can be seen that the fractal dimensions at different positions perpendicular to the orientation direction are 1.8228 and 1.8332 respectively, and the difference in fractal dimensions is within the range of 0 < δ ≤ 0.02, indicating that the magnet of Example 1 is uniform in the direction perpendicular to the orientation.

[0097] The difference in fractal dimensions of the magnet of Example 1 in the direction parallel to the orientation and the direction perpendicular to the orientation is > 0.05, indicating that the magnet is anisotropic and indicates that the magnet has high remanence and low coercivity.

[0098] After being detected by a permanent magnet material measurement system, the test performance of the magnet in Example 1 is shown in Table 1 below. The maximum difference in remanence at different positions is 0.02 kGs, and the deviation of remanence at different positions (the maximum difference in remanence / average value) = 0.14% < 1% (it is considered uniform within 1%). It can be seen that the magnet in this example is uniform; the coercivity is greater than 8 kOe (if the coercivity is greater than 8 kOe, it is anisotropic), so it can be seen that the magnet is anisotropic. The coercivity is 12.10 - 12.13 kOe, and the remanence is 14.19 - 14.21 kGs. It can be seen that the magnet has high remanence and low coercivity.

[0099] It can be seen that the characterization of the permanent magnet material by the characterization method of the present invention is consistent with the actual results.

[0100] Table 1 Test performance of the magnet in Example 1

[0101]

[0102] Example 2

[0103] This example provides a method for characterizing the microstructure and magnetic properties of a permanent magnet material. The permanent magnet material in this example is 30EH. The method in this example includes the following steps:

[0104] Step 1: Compress the specimen with a universal testing machine to obtain a fracture specimen;

[0105] Step 2: Clean the fracture with acetone;

[0106] Step 3: Observe the fracture with a scanning electron microscope, and collect micrographs of different positions in the direction parallel to the orientation and micrographs of different positions in the direction perpendicular to the orientation;

[0107] Step 4: Calculate the fractal dimension of the micrographs using the fractal dimension calculation method;

[0108] Step 5: Evaluate the uniformity, isotropy or anisotropy, and magnetic properties of the permanent magnet material according to the fractal dimensions of the micrographs at different positions. The fractal dimensions at different positions in two directions are used to judge the uniformity, and the average value of the fractal dimensions at different positions in two directions is used to judge the isotropy or anisotropy and the evaluation of magnetic properties;

[0109] Figure 5 and Figure 6They are the results of Location 1 and Location 2 randomly selected on the fracture surface of Example 2 parallel to the orientation direction. Among them, (a) is the scanning electron microscope photo, (b) is the binary image after image processing using the box-counting method, (c) is the data fitting of different box side lengths after image processing using the box-counting method, and (d) is the fractal dimension of different box side lengths after image processing using the box-counting method. Among them, the scanning electron microscope photo includes a gray main phase and a bright white rare-earth-rich grain boundary phase.

[0110] Figure 7 and Figure 8 They are the results of Location 1 and Location 2 randomly selected on the fracture surface of Example 2 perpendicular to the orientation direction. Among them, (a) is the scanning electron microscope photo, (b) is the binary image after image processing using the box-counting method, (c) is the data fitting of different box side lengths after image processing using the box-counting method, and (d) is the fractal dimension of different box side lengths after image processing using the box-counting method. Among them, the scanning electron microscope photo includes a gray main phase and a bright white rare-earth-rich grain boundary phase.

[0111] From Figure 5 and Figure 6 it can be seen that the fractal dimensions at different positions parallel to the orientation direction are 1.7806 and 1.7935 respectively, and the difference in fractal dimensions is within the range of 0 < δ ≤ 0.02, indicating that the magnet of Example 2 is uniform in the direction parallel to the orientation.

[0112] From Figure 7 and Figure 8 it can be seen that the fractal dimensions at different positions perpendicular to the orientation direction are 1.8146 and 1.8246 respectively, and the difference in fractal dimensions is within the range of 0 < δ ≤ 0.02, indicating that the magnet of Example 2 is uniform in the direction perpendicular to the orientation.

[0113] The average value of the difference in fractal dimensions of the magnet of Example 2 in the direction parallel to the orientation and the direction perpendicular to the orientation is between 0.03 and 0.05, indicating that the magnet is anisotropic, and indicating that the magnet has high coercivity and low remanence.

[0114] After being detected by a permanent magnet material measurement system, the test performance of the magnet of Example 2 is shown in Table 2 below. The maximum difference in remanence at different parts is 0.02 kGs, and the remanence deviation at different parts (the maximum difference in remanence / average value) = 0.18% < 1% (within 1% is considered uniform). It can be seen that the magnet of this example is uniform; the coercivity is greater than 8 kOe (if the coercivity is greater than 8 kOe, it is anisotropic), it can be seen that the magnet is anisotropic, the coercivity is 30.10 - 30.20 kOe, and the remanence is 11.18 - 11.20 kGs. It can be seen that the magnet has high coercivity and low remanence.

[0115] It can be seen that the characterization of the permanent magnet material by the characterization method of the present invention is consistent with the actual results.

[0116] Table 2 Test performance of the magnet in Example 2

[0117]

[0118] Example 3

[0119] This example provides a method for characterizing the microstructure and magnetic properties of a permanent magnet material. The permanent magnet material in this example is Is20, and the method in this example includes the following steps:

[0120] Step 1: Compress the specimen with a universal mechanical testing machine to obtain a fractured specimen;

[0121] Step 2: Clean the fracture with acetone;

[0122] Step 3: Observe the fracture with a scanning electron microscope, and collect micrographs of different positions in the direction parallel to the orientation and micrographs of different positions in the direction perpendicular to the orientation;

[0123] Step 4: Calculate the fractal dimension of the micrographs using the fractal dimension calculation method;

[0124] Step 5: Evaluate the uniformity, isotropy or anisotropy, and magnetic properties of the permanent magnet material according to the fractal dimensions of the micrographs at different positions;

[0125] Figure 9 and Figure 10 are the results of position one and position two randomly selected on the fracture in the direction parallel to the orientation in Example 3, respectively. Among them, (a) is a scanning electron microscope photo, (b) is a binary image after image processing using the box-counting method, (c) is the data fitting of different box side lengths after image processing using the box-counting method, and (d) is the fractal dimension of different box side lengths after image processing using the box-counting method; among them, the scanning electron microscope photo includes a gray main phase and a bright white rare-earth-rich grain boundary phase.

[0126] Figure 11 and Figure 12 are the results of position one and position two perpendicular to the orientation direction on the fracture in Example 2, respectively. Among them, (a) is a scanning electron microscope photo, (b) is a binary image after image processing using the box-counting method, (c) is the data fitting of different box side lengths after image processing using the box-counting method, and (d) is the fractal dimension of different box side lengths after image processing using the box-counting method; among them, the scanning electron microscope photo includes a gray main phase and a bright white rare-earth-rich grain boundary phase.

[0127] From Figure 9 and Figure 10It can be seen that the fractal dimensions at different positions parallel to the orientation direction are 1.7987 and 1.8111 respectively, and the difference in the fractal dimensions is within the range of 0 < δ ≤ 0.02, indicating that the magnet of Example 3 is uniform in the direction parallel to the orientation.

[0128] From Figure 11 and Figure 12 it can be seen that the fractal dimensions at different positions perpendicular to the orientation direction are 1.8040 and 1.8155 respectively, and the difference in the fractal dimensions is within the range of 0 < δ ≤ 0.02, indicating that the magnet of Example 3 is uniform in the direction perpendicular to the orientation.

[0129] The average value of the difference in the fractal dimensions of the magnet of Example 3 in the direction parallel to the orientation and the direction perpendicular to the orientation < 0.03, indicating that the magnet is isotropic.

[0130] After being detected by a permanent magnet material measurement system, the test performance of the magnet of Example 3 is as shown in Table 3 below. The maximum difference in the remanence of different parts is 0.02 kGs, and the remanence deviation of different parts (the maximum difference in remanence / average value) = 0.12% < 1% (it is considered uniform within 1%), so it can be seen that the magnet of this example is uniform; the coercive force is less than 8 kOe (if the coercive force is greater than 8 kOe, it is anisotropic), so it can be seen that the magnet is isotropic.

[0131] It can be seen that the characterization of the permanent magnet material by the characterization method of the present invention is consistent with the actual results.

[0132] Table 3 Test performance of the magnet of Example 3

[0133]

[0134] Example 4

[0135] This example provides a method for characterizing the microstructure and magnetic properties of a permanent magnet material. The permanent magnet material of this example is 40UH, and the method of this example includes the following steps:

[0136] Step 1: Polish the surface of the sample by argon ion polishing to obtain a specimen;

[0137] Step 2: Select positions using a scanning electron microscope, and use a probe to collect EBSD photos in the direction perpendicular to the orientation and EBSD photos in the direction parallel to the orientation;

[0138] Step 4: Calculate the fractal dimension of the EBSD photo using a fractal dimension calculation method;

[0139] Step 5: Evaluate the uniformity, isotropy or anisotropy, and magnetic properties of the permanent magnet material based on the fractal dimensions of the EBSD photographs at different positions. The fractal dimensions at different positions in two directions are used to judge the uniformity, and the average of the fractal dimensions at different positions in two directions is used to judge the isotropy or anisotropy and evaluate the magnetic properties;

[0140] Figure 13 and Figure 14 are the results of position one and position two randomly selected from the EBSD photograph perpendicular to the orientation direction in Example 4, where (a) is the EBSD photograph, (b) is the binary image after image processing using the box-counting method, (c) is the data fitting of different box side lengths after image processing using the box-counting method, and (d) is the fractal dimension of different box side lengths after image processing using the box-counting method.

[0141] Figure 15 and Figure 16 are the results of position one and position two randomly selected from the EBSD photograph parallel to the orientation direction in Example 4, where (a) is the EBSD photograph, (b) is the binary image after image processing using the box-counting method, (c) is the data fitting of different box side lengths after image processing using the box-counting method, and (d) is the fractal dimension of different box side lengths after image processing using the box-counting method.

[0142] From Figure 13 and Figure 14 it can be seen that the fractal dimensions at different positions parallel to the orientation direction are 1.7463 and 1.7475 respectively, and the difference in fractal dimensions is within the range of 0 < δ ≤ 0.02, indicating that the magnet in Example 4 is uniform in the direction parallel to the orientation.

[0143] From Figure 15 and Figure 16 it can be seen that the fractal dimensions at different positions perpendicular to the orientation direction are 1.7805 and 1.7826 respectively, and the difference in fractal dimensions is within the range of 0 < δ ≤ 0.02, indicating that the magnet in Example 4 is uniform in the direction perpendicular to the orientation.

[0144] The average of the differences in the fractal dimensions of the magnet in Example 4 in the direction parallel to the orientation and the direction perpendicular to the orientation is between 0.03 and 0.05, indicating that the magnet is anisotropic and indicating that the magnet has high coercivity and low remanence.

[0145] After being detected by the permanent magnet material measurement system, the test performance of the magnet in the embodiment is shown in Table 4 below. The maximum difference in the remanence of different parts is 0.02 kGs, and the deviation of the remanence of different parts (the maximum difference in remanence / average value) = 0.16% < 1% (it is considered uniform within 1%). It can be seen that the magnet in this embodiment is uniform; the coercivity is greater than 8 kOe (if the coercivity is greater than 8 kOe, it is anisotropic), so it can be seen that the magnet is anisotropic. The coercivity is 25.31 - 25.34 kOe, and the remanence is 12.48 - 12.50 kGs. It can be seen that the magnet has high coercivity and low remanence.

[0146] It can be seen that the characterization of the permanent magnet material by the characterization method of the present invention is consistent with the actual results.

[0147] Table 4 Test performance of the magnet in Example 4

[0148]

[0149] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for characterizing the microstructure and magnetic properties of a permanent magnet material, characterized in that, The characterization method includes: Collecting microscopic morphology photos of different positions of the permanent magnet material; the microscopic morphology is the scanning electron microscope microstructure morphology of the fracture specimen and / or the electron backscatter diffraction microscopic morphology of the planar metallographic specimen; Calculating the fractal dimension of the microscopic morphology photos by using the fractal dimension calculation method; Judging the uniformity, isotropy or anisotropy, and magnetic properties of the permanent magnet material according to the fractal dimensions of the microscopic morphology photos at different positions; Among them, the uniformity of the permanent magnet material is judged according to the absolute value of the difference in the fractal dimensions of the microscopic morphology photos at different positions on the same plane; the isotropy or anisotropy and magnetic properties of the permanent magnet material are judged according to the absolute value of the difference in the fractal dimensions in the vertical orientation direction and the parallel orientation direction of the material; The magnetic properties mainly include remanence and coercivity; The method for judging the isotropy or anisotropy of the permanent magnet material according to the absolute value of the difference in the fractal dimensions in the vertical orientation direction and the parallel orientation direction of the material includes: When Δ≥0.03, the permanent magnet material is anisotropic; When 0≤Δ≤0.03, the permanent magnet material is isotropic; The method for judging the magnetic properties of the permanent magnet material according to the absolute value of the difference in the fractal dimensions in the vertical orientation direction and the parallel orientation direction of the material includes: When Δ≥0.05, the permanent magnet material has high remanence and low coercivity; When 0.03≤Δ<0.05, the permanent magnet material has high coercivity and low remanence; High remanence means that the remanence is in the range of 14.0 kGs to 15.5 kGs, and low coercivity means that the coercivity is in the range of 8.0 kOe to 14.0 kOe; low remanence means that the remanence is in the range of 10.0 kGs to 14.0 kGs, excluding 14.0 kGs; high coercivity means that the coercivity is in the range of 14.0 kOe to 45.0 kOe, excluding 14.0 kOe.

2. The method for characterizing the microstructure and magnetic properties of the permanent magnet material according to claim 1, characterized in that The method for judging the uniformity according to the absolute value of the difference in the fractal dimensions of the microscopic morphology photos at different positions on the same plane includes: When 0≤δ≤0.02, the permanent magnet material is uniform; When δ>0.02, the permanent magnet material is non-uniform.

3. The method for characterizing the microstructure and magnetic properties of the permanent magnetic material according to claim 1, wherein The permanent magnet material includes rare earth permanent magnet materials, ferrite permanent magnet materials or alnico permanent magnet materials.

4. The method for characterizing the microstructure and magnetic properties of the permanent magnet material according to any one of claims 1 to 3, characterized in that, Calculating the microscopic morphology photos by using the fractal dimension calculation method includes: first performing binarization processing on the obtained microscopic morphology photos through a computer-aided program, and the information of the picture is converted into a matrix containing only 0 and 1; then using image processing technology to process and analyze the image, so as to obtain the fractal dimension.

5. The method for characterizing the microstructure and magnetic properties of the permanent magnet material according to claim 4, wherein, The image processing technology includes the direct counting method, the box counting method, the differential box method, and the small vein method.

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